The present invention relates to a wire sawing device comprising at least one layer of wires adapted to move with alternate or continuous movement, this layer of wires being pressed against a piece to be sawed and supported by wire guide cylinders, first means being provided to carry out a relative advancing movement between the piece to be sawed and the layer of wires in a cutting direction contained in a cutting plane, second means being provided to carry out a relative oscillating movement between the piece to be sawed and the layer of filaments about an axis of oscillation perpendicular to the cutting plane.
In this type of device, the filament is wound spirally about wire guide cylinders and forms between two wire guide cylinders at least one layer of parallel wires whose distance between successive wires fixes the thickness of the slices. Moreover, the plane of the layer or layers of wires forms, in known devices, a fixed angle generally perpendicular to the direction of sawing, which can give rise to undulations and striations on the surface of the slices in the case of generally lateral movement of the layer of wires resulting from thermal oscillations for example. These undulations, even though several micrometers in amplitude, suffice to render unusable the slices for certain applications such as silicon for the semiconductor industry. Moreover, during use of the back and forth movements, a roughness due to the reversal of direction arises. The tendency of the users of slices is to specify that these have a rough sawed surface as perfect as possible so as to reduce the subsequent operations of lapping or correction and polishing. Moreover, during the use of free abrasive, the abrasive picked up by the wire will become worn along the length of the sawing path and hence will modify the width of the sawed line. This wear will as a result give rise to a variation in the thickness of the slices. The sawing results as well as the tolerances obtained will depend on the penetration of the abrasive between the wire and the piece to be sawed as well as its wear along the sawing path. This wear of the abrasive will depend on the type of abrasive and on the length of the sawed or engaged length, which is to say the dimension of the ingots. This dimension being constantly increasing because of the progress of the technology of crystal growth, the phenomenon has a tendency to accentuate itself. It will also depend on the quantity of material removed per unit length and per unit time. During cutting of the pieces of non-rectangular or square shape, the length sawed by the layer of filaments or length engaged, varies as a function of the sawing depth. The penetration of the abrasive, and hence the wear of the abrasive, will thus vary as a function of the sawed height, giving rise in the shape of the piece to a variation of thickness which is a function of the height. This variation of thickness can be sufficiently great that the tolerances given by the user will be exceeded.